The Difference between Colour-coated Galvanised Aluminium Coils And Colour-coated Aluminium Coils

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The Difference between Colour-coated Galvanised Aluminium Coils And Colour-coated Aluminium Coils

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1. Colour-coated galvanised aluminium coil

Base material: Galvanised aluminium steel sheet (typically with a hot-dip galvanised aluminium alloy coating, such as an aluminium-zinc alloy coating, with typical composition of 55% aluminium + 43.4% zinc + 1.6% silicon, etc.), with an organic coating applied to the surface (such as polyester, fluorocarbon, etc.).

Production process: Galvanised aluminium substrate → Surface pre-treatment (degreasing, chemical conversion) → Roll coating or spray coating with coloured coating → Drying and curing → Finished product.

2. Colour-coated aluminium coils

Substrate material: Pure aluminium or aluminium alloy (e.g., Series 1 pure aluminium, Series 3 aluminium-manganese alloy, Series 5 aluminium-magnesium alloy, etc.), with a colour-coated layer applied to the surface.

Process flow: Aluminium substrate → Surface treatment (degreasing, chemical oxidation or chromating) → Coating (single or multi-layer coating) → Curing and forming.

Core Performance Comparison

Dimension	Colour-coated galvanised aluminium coil	Colour-coated aluminium coil
Material properties	The substrate is steel-based + galvanised aluminium coating, combining the strength of steel with the corrosion resistance of aluminium-zinc.	Pure aluminium or aluminium alloy substrate, low density (approximately 2.7 g/cm³), lightweight, excellent electrical conductivity and thermal conductivity.
Corrosion Resistance	The galvanised aluminium coating (e.g., aluminium-zinc alloy) offers superior corrosion resistance compared to pure galvanised steel sheets in humid or acidic/alkaline environments, but may rust when exposed to highly corrosive media over extended periods.	The aluminium substrate naturally forms a dense oxide film on its surface, providing strong corrosion resistance, particularly against atmospheric corrosion, making it suitable for coastal areas or industrial pollution zones.
Weight and Strength	High density (approximately 7.85 g/cm³) and high strength, suitable for load-bearing structures.	Low density, with strength adjustable based on alloy type (e.g., 5 series), good flexibility, and strong resistance to deformation.
High-Temperature Resistance	The melting point of the galvanised aluminium coating is relatively low (approximately 560°C for aluminium-zinc alloys), and the coating may fail at high temperatures.	Pure aluminium has a melting point of approximately 660°C, and aluminium alloys exhibit superior high-temperature resistance compared to galvanised aluminium coils, making them suitable for applications requiring heat resistance.
Coating adhesion	After surface treatment, the coating adhesion on galvanised aluminium substrates is good, but differences in thermal expansion coefficients between the steel substrate and the coating may cause cracking over time.	Aluminium substrates have more compatible thermal expansion coefficients with the coating, resulting in more stable adhesion and better weather resistance.

Cost and Maintenance

Cost Comparison: Colour-coated galvanised aluminium coils typically cost less than colour-coated aluminium coils due to the lower cost of steel-based materials. Colour-coated aluminium coils, however, are more expensive due to the higher cost of aluminium materials and the frequent use of high-end coatings (such as fluorocarbon).

Maintenance Requirements: Colour-coated galvanised aluminium coils may rust if the coating is damaged and require timely repairs; colour-coated aluminium coils have a strong self-healing oxide film on their surface, resulting in lower maintenance costs and greater long-term cost-effectiveness.

Select application scenarios according to demand

Application Areas	Colour-coated galvanised aluminium coils	Colour-coated aluminium coils
Construction Engineering	Ordinary factory roofs, interior wall panels (cost-effective, moderate corrosion resistance)	Curtain walls, exterior wall decorative panels, coastal buildings (salt spray resistance, aesthetic durability)
Transportation Industry	Truck body floors (high strength), ordinary car bodies	High-speed rail interiors, ship decks, new energy vehicle battery cases (lightweight + corrosion resistance)
Home Appliances and Electronics	Refrigerator back panels, air conditioner outdoor units (cost-effectiveness priority)	High-end appliance panels， heat sinks (good thermal conductivity)
Special Environments	Rural dwellings, outdoor facilities in non-humid regions	Chemical plants, marine engineering, acid rain areas (chemical corrosion resistance)

Service life:

Galvanised aluminium coils: ordinary polyester coating has a service life of approximately 10-15 years in a neutral environment and requires repair after damage;

Aluminium coils: fluorocarbon coating (PVDF) can be used outdoors for 20-30 years, and the self-repairing ability of the oxide film extends the service life of the substrate, resulting in lower overall costs.

Can the differences between colour-coated galvanised aluminium coils and colour-coated aluminium coils be distinguished by their surfaces?

Visual comparison of surface characteristics

1. Colour and gloss: No absolute differences, but details can be discerned

Common features: Both can be customised in the same colour family (e.g., silver-grey, sea blue, brick red, etc.), and there is no fundamental difference in gloss (matte/glossy). Simply looking at the colour cannot distinguish between them.

Hidden clues:

Colour-coated galvanised aluminium coils: Due to the higher density of the steel substrate, the coils are heavier at the same thickness, resulting in a noticeable difference in feel during handling;

Colour-coated aluminium coils: Aluminium has a slight ‘metallic coolness’ in its gloss, especially silver-white coils, which reflect light more softly under sunlight (steel substrates have a harsher reflection).

2. Surface defects and process marks

Colour-coated galvanised aluminium coils:

May exhibit ‘zinc flower’ marks (crystalline patterns formed during the cooling of the galvanised aluminium coating, resembling snowflakes, commonly found on unfinished substrates);

If the coating is damaged, the exposed underlying layer is silver-grey galvanised aluminium, with possible minor rust stains along the edges (after prolonged exposure).

Colour-coated aluminium coils:

No zinc flowers on the surface; the substrate colour is silver-white (pure aluminium) or slightly metallic in hue (e.g., 3-series aluminium-manganese alloy appears pale golden);

If the coating is damaged, the exposed aluminium substrate shows no rust stains; after oxidation, it forms a greyish-white powdery substance (Al₂O₃), rather than the reddish-brown colour of iron rust.

Practical methods for quick differentiation

Testing Method	Colour-coated galvanised aluminium coil	Colour-coated aluminium coil
Weight Perception	Significantly heavier than other materials of the same size , with a noticeable difference when held in one hand	Lightweight, with sheets of the same thickness easily lifted with one hand
Magnetic Test	Steel substrate can be attracted by a magnet (galvanised aluminium layer does not affect magnetism)	Aluminium substrate is non-magnetic, and magnets do not adhere at all
Bending test	When forcibly bent, the coating may develop small cracks and the bent area may turn white	Good flexibility; the coating is less likely to crack when bent at large angles, and the substrate exhibits silver-white bending marks.
Scratch test	When lightly scraping the damaged coating with a coin, the underlying layer is silver-grey metal, and the edges of the scratch may turn black (steel oxidation).	he underlying layer of the scratch is silver-white aluminium, with no blackening, and turns white-grey after oxidation.